FREE FLIGHT INTERVIEWS HP-19 BUILDER
Henery Preiss, January 1981
by Tony Burton
A lot of rumours have been circulating about the newest glider expected to appear out of the Schreder "Skunkworks" in Bryan, Ohio. It turns out that Henry Preiss, who was recently president of the Windsor Glinding Club for five years, and now manages Dick Schrederís drafting instruments company, will be the only builder of the HP-19. The glider to appear for homebuilders will be called the HP-20. Henry was contacted by telephone on 6 January to tell us whatís going on:
FF: Good morning, Henry. We have been getting conflicting information about progress on the HP-19. All we know for certain now is that it is going to be an all-metal, T-tail, 15 metre ship, with a new airfoil. We saw the beginnings of the fuselage when we passed through Bryan last April. We understand that you have become involved in the production of the prototype. How did that come about?
HENRY: Well, I had experience in glider construction. I built the RHJ-8 2-place which you can see in the new SAC calendar and I am now flying its successor, the RHJ-9, which I also designed and built. Last year Dick asked me if I would help him in working on the HP-19 prototype. I agreed providinq that two were built, one for me and one for him. I thought that I would have a lot more incentive to work on the project if I got something tangible out of the process.
FF: We heard that two different wings are being built for the HP-19. Can you explain that?
HENRY: Considerable design work was done on a wing similar to the HP-18 or RS-15 wing, but using a new airfoil and a carbon spar. After the wing construction had begun, Dick had second thoughts; it was going to be prohibitively expensive to supply carbon spars in kits, and new wing planforms with double taper were coming out in Germany which promised less plan induced drag. So the wing was started over. Rather than abandon the old work, I proposed to complete the wing for my glider. Dick would then be able to compare performance with his prototype carrying the updated wing design when both got flying. The new glider would be called the HP-20.
FF: So you have the only living HP-19?
FF: What exactly is the dIfference between the two wings?
HENRY: The HP-20 wing will employ a metal box-spar, and have a double taper, and be smaller at just over 100 square feet. The HP-19 will use the carbon spar (the only one built) which was originally intended for use on a proposed "light weight" HP-18A which was never developed. This wing has an area of about 108 square feet.
FF: Can you tell us more about the new airfoil?
HENRY: A lot of work was done between Dick and Columbus University, I believe, on a computer assisted design. The university had 2 or 3 people involved in the project. After a good number of runs through the computer, Dick has an airfoil he is satisfied with. It has some resemblance to the Wortmann airfoils, but has a more rounded leading edge. Itís about 18% thick I bel ieve.
FF: Was Dick looking for an airfoil that was a bit more forgiving to construct? There has been a lot of talk of skin separation under the leading edge of the HP-18 wings.
HENRY: Dick is a bit sensitive on the subject, which he believes has been exaggerated a great deal. I doubt that was a consideration in the design; the lower surface contour is very similar to the one used on the HP-18, and was the result of the aerodynamic optimization of the airfoil using the computer.
FF: Letís talk about the rest of the glider. We saw the fuselage in its early stages of construction. It looked somewhat like a "low-profile" HP-11.
HENRY: Yes. Itís aII-metal with a tapered cone rear fuselage, and uses the stretched skins of the HP-16 for the forward portion. The seat back reclines about forty-five degrees.
FF: Why did Dick decide to go with a T-tail configuration? The V-tail has almost been his trademark.
HENRY: Its entirely a marketing decision. T-tails sell better than V-tails, although there is no difference in performance. We still are convinced that the V-tail is more efficient, simpler to build, lighter, and has better ground clearance and gives less chance of damage to fuselage in a ground loop due to its smaller moment of inertia.
FF: Will the flap and aileron be interconnected?
HENRY: I donít know. I just saw some of the initial design drawings. If I can figure out what all the cranks are for, I may install it.
FF: How far along are you now?
HENRY: Well, the wings are done and the fuselage is about 75% complete. I expect to get it flying in the early spring.
FF: Well Henry, good luck on your HP-19, and we look forward to hearing more of the HP-20. I hope youíll write us a story soon with some pictures for FREE FLIGHT on your building efforts.